Motor fuel containing octane appreciator



United States Patent 3,087,802 MOTDR FUEL CONTAINING OCTANE APPRECIATORHarry Chafetz, Poughkeepsie, and George W; Eckert, Wappingers Falls,N.Y., assignors to Texaco Inc., New York, N.Y., acorporation of DelawareNo Drawing. Filed Nov. 25, 1959, Ser. No. 855,268 9 Claims. (Cl. 4469)This invention relates to a hydrocarbon fuel composition of high octanerating. More specifically, it involves the discovery that theoctanerating of leaded gasoline fuels is substantially improved bytheaddition of O-acyl alkyl carbonates.

The recent increases in compression ratios of automobile engines haveplaced a severe strain on petroleum refiners to produce fuels having theoctane ratings demanded by these engines. Premium'fuels at the presenttime have research octane ratings between 97 and 101 and it has beenpredicted that premium fuels will have to have octane ratings between105 and 110 five years from now in order to satisfy theoctane'requirements of the high compression automotive engines predictedfor that date. In order to produce premium fuels of octane ratings of 95and above, it has been necessary for refiners to rely heavily oncatalytic refining operations such as fluid catalytic cracking,catalytic reforming, alkylation and catalytic isomerization.

Catalytic cracking and catalytic reforming, which are the most widelyused refining operationsin the production of high octane fuels, producesubstantial quantities of aromatics; catalytic cracking also produces asubstantial amount of olefins. It is well known that olefins andaromatics, although possessing high octane ratings, have a poorerresponse to organo-lead compounds such as tetraethyl lead than saturatedaliphatic gasoline components. Accordingly, as the aromatic and olefiniccontentof the gasolines have increased to meet the octane levelsrequired by modern automotive high compression engines, the leadresponse of the resulting fuels has diminished.

,Stated' another way, the octane increment obtainable by the addition ofan organo-lead compound decreases as the aromatic andolefin contents ofthe base fuel increase. The subject invention involves the discoverythat the octane rating of leaded moto'r fuels containing a substantialconcentration of high octane components, that'is, aromatic, olefins andmixtures thereof, is markedly improved by the addition of a small amountof O acyl alkyl oarbonatesn In a commonly-assigned copendingapplication, Serial No. 689,466, filed October 11, 1957', by G. W.Eckert, it is disclosed that hydrocarbyl monocarboxylic acidssubstantially raise the octane rating of a motor fuel containing anorgan c-lead anti-knock agent and a substantial concentration'of highoctane components which may be aromatic hydrocarbons, olefinichydrocarbons or mixtures thereof. In a series of cases filed subsequentto the afore-identified copending application it is disclosed that thisoctane appreciating action in:the leaded fuels of prescribed compositionis also possessed by a number of acid derivatives such as tertiary alkylesters and acid anhydrides which are converted to hydrocarbylmonoc-arboxylic acids at the conditions prevailing in the engine duringcombustion. The subject invention involves the discovery that O-acylalkyl carbonates also have an octane appreciating action in leaded motorfuel compositions of this type.

The high octane hydrocarbon motor fuel of this invention com-prises highoctane components including a substantial concentration of aromatichydrocarbons, olefinic hydrocarbons and mixtures thereof, an organo-leadanti- "ice knock agent, and an O-acyl alkyl carbonate which is a mixedanhydride of a hydrocarbyl monocarboxylic acid containing 2-30 carbonatoms and an alkyl hydrogen carbonate in which said alkyl group.contains 1-10 carbon atoms. The O-acyl alkyl carbonates act as octaneappreciators in leaded fuels of prescribed composition when presenttherein in concentrations between 0.1 and 5.0 volume percent.

The action of these O-acyl alkyl carbonates in appreciating theoctane'rating of gasoline is characterized by several unusual features.In the first instance, these compounds are ineifective in raising theoctane rating of gasoline unless an organo-lead anti-knock agent,normally tetraethyl lead, TEL, is a component of the gasoline'mixture.The second unusual characteristic of their action in appreciating theoctane rating of gasoline is the fact that an equivalent concentrationof O-acyl alkyl carbonates causes a greater octane improvement above the100 oc tane level than below the 100 octane level. The third unusualfeature of the action of these O-acyl 'alkyl carbonates is that theyappear to have substantially little effect on the octane rating of agasoline consisting essentially of saturated aliphatic hydrocarbons eventhough an organo-lead anti-knock agent is present.

Since organo-lead anti-knock agents exert their greatest octaneappreciation in predominantly saturated paraifinic base hydrocarbongasolines and have the least effect on the octane rating of aromatic andolefin-rich gasolines, the present invention neatly complementstetraethyl lead as an octane improver. Oaacyl alkyl carbonates havetheir minimum effect where tetraethyl lead has its maximum effect andexert their maximum effect on octane values where tetraethyl lead hasits minimum effect.

The novel fuel compositions of this invention have a minimumconcentration of aromatic and/ or olefin components of at least 5 Volumepercent. The aromatic and/ or olefin components of the motor fuel of theinvention can constitute as high as 100 volume percent thereof butusually comprise between 20 and 80 volume percent. A 5 percentconcentration of aromatics and/or olefins appears to be necessary for Oacyl alkyl carbonates to exert a significant octane improvement.

The aromatic components of the motor fuel of the invention are generallysupplied by catalytic reforming or catalytic cracking operations.Catalytic ateform alte is particularly high in aromatics. The olefincomponents of the motor fuel of the invention are derived either fromthermal cracking, catalytic crackingor polymerization.

The organo-lead reagent necessary for the action of O-acyl alkylcarbonates as octane improvers is usually a tetraalkyl lead compound.Tetraethyl lead is universally used as an anti-knock agent but othertetraalkyl lead compounds such as tetramethyl lead, tetrabutyl lead,tetraa-myl lead, tet-rap-ropyl lead, etc., possess anti-knock propertiesand may be used in the fuel compositions of the invention in conjunctionwith O-acyI alkyl carbonates.

The tetraethyl lead mixtures commercially available for automotive usecontain an ethylene chloride-ethylene bromide mixture as a scavenger forremoving lead from the combustion chamber in the form of volatileleadhalides. iTetraethyl lead fluid, the commercial product, comprisestetraethyl lead, ethylene chloride and ethylene bromide, the latter tworeagents being present in 1.0 theory and 0.5 theory, respectively,theory denoting, the stoichiometric amount required for reaction withthe lead content of the tetraethyllead.

The organo-lead regeant is present in the fuel compositions of theinvention in concentrations between 0.5 ml. per gallon up to thestatutory limit of organo-l'ead reagent concentration which, at thepresent time, is 4 ml. per gallon in the case of automotive fueland.4.6- ml. per gallon in the case of aviation fuel. The usualconcentration of tetraethyl lead is between 1 and 3 ml. per gallon inautomotive gasoline and 2 to 4.6 ml. per gallon in aviation gasoline. Anoctane appreciating action is obtained with O-acyl alkyl carbonates atTEL concentrations of 6 ml. per gallon and higher.

The O-acyl alkyl carbonates which are effective in increasing the octanerating of aromatic and olefin-containing leaded gasoline are mixedanhydrides of a hydrocarbyl monocarboxylic acid containing 230 carbonatoms and an alkyl hydrogen carbonate in which the alkyl group contains1-10 carbon atoms. These mixed anhydrides are readily prepared byreaction of hydrocarbyl monocarboxylic acids with chlorofor-mate estersin the presence of an amine hydrogen chloride acceptor such as pyridine.The preparation of these mixed anhydrides is illustrated by theformation of O-acetyl ethyl carbonate by reaction of acetic acid withethyl c'hloroformate as shown in the following equation:

Pyridine H OHaC-O C-OCzH 1101 011300 OH Gi -002135 The O-acyl alkylcarbonates effective as octane appreciators are represented by thegeneral formula:

wherein R denotes a hydrocarbyl radical containing 1-29 carbon atoms andR is an alkyl group containing 1-10 carbon atoms. Preferably, R is analiphatic or aryl 11ydrocarbyl radical containing 1-10 carbon atoms andR is an alkyl group containing 1-6 carbon atoms.

Examples of O-acyl alkyl carbonates effective as octane appreciators inleaded fuels or prescribed composition are the following: O-acetylmethyl carbonate, O-acetyl ethyl carbonate, O-propionyl ethyl carbonate,O-propionyl butyl carbonate, O-benzoyl n-butyl carbonate, O-butyrylethyl carbonate, O-Z-ethylhexanoyl ethyl carbonate, O-lauroyl ethylcarbonate, O-n-pentanoyl isopropyl carbonate, O-acetyl isopropylcarbonate, O-heptanoyl methyl carbonate, O-acetyl 2-ethylhexylcarbonate, O-acetyl t-butyl carbonate, O-propionyl decyl carbonate.

The effectiveness of O-acyl alkyl carbonates as octane appreciators isbelieved to result from the fact that they decompose to form hydrocarbylmonocarboxylic acids under the conditions existing during oxidation ofthe gasoline in the internal combustion engine.

The O-acyl alkyl carbonates must be present in the leaded aromatic and/or olefin-containing compositions of the invention in a minimumconcentration of 0.1 volume percent before a significant octaneappreciation is realized. When the concentration of the esters is below0.1 volume percent, there is no noticeable octane improvement in leadedgasolines of prescribed composition. The preferred concentration ofO-acyl alkyl carbonates falls between 0.2 and 2.0 volume percent withmaximum octane appreciation generally being obtained at concentrationsbetween 0.5 and 1.5 volume percent. Although concentrations of the esterof O-acyl alkyl carbonates as high as 5 volume percent may be employed,economic considerations preclude the use of such high concentrations. Inaddition, it appears that there is a significant decrease in octaneappreciating action after the ester concentration exceeds about 2.0volume percent.

In Table I there is shown the effectiveness of the O-acyl alkylcarbonates of prescribed composition in raising the octane rating of aleaded fuel composition containing the prescribed aromatic and/0r olefincontent. The base fuel employed in Table I had a Research Octane Number(RON) of 105, a Motor Octane Number (MON) of 98.5 and comprisedapproximately volume percent n-butane, 40 percent isobutyIene-isobutanealkylate, 10 percent pentenes from fluid catalytically cracked naphthaand 40 percent heavy platformate; the base fuel contained 3 cc. of TELper gallon. Fluorescent indicator analysis (FIA) of the 105 octane basefuel indicated an aromatic content of approximately 35 percent and anolefin content of approximately 6 percent; its initial boiling point(IBP) was F. and its end point was 367 TABLE I Octane Increase in RONFuel by O-Acyl Alkyl Carbonates Increase in RON Base fuel +0.5 v.percent propionyl ethyl carbonate 1.7 Base fuel +0.75 v. percentpropionyl ethyl carbonate 3.1 Base fuel +1.0 v. percent propionyl ethylcarbonate 2.7 Base fuel +0.5 v. percent O-n-butyryl ethyl carbonate 0.2Base fuel +0.75 v. percent O-n-butyryl ethyl carbonate 0.8

Base fuel +1.0 v. percent O-n-butyryl ethyl carbonate 1.0

The data in the above table show the effectiveness of O-acyl alkylcarbonates in appreciating the octane rating of leaded fuels containingthe prescribed aromatic and/ or olefin content.

In Table II there is shown the octane appreciating action of O-acylalkyl groups in a commercial premium motor fuel having an RON of 100.3.The premium motor fuel employed in Table II contained 3 cc. of TEL/ gal.and had an IBP of 89 F., and an end point of 372 F. 'FIA indicated thatit comprised approximately 53% saturated hydrocarbons, 38% aromatics and9% olefinic hydrocarbons.

TABLE II Octane Increase in Premium Fuel by O-Acyl Alkyl CarbonalesIncrease in RON Base fuel +0.5 v. percent propionyl ethyl carbonate" 0.4

Base fuel +0.75 v. percent propionyl ethyl carbonate 0.6 Base fuel +1.0v. percent propionyl ethyl carbonate 1.2 Base fuel +0.5 v. percentO-n-butyryl ethyl carbonate 0.2 Base fuel +0.75 v. percent O-n-butyrylethyl carbonate 0.4

Base fuel +1.0 v. percent O-n-butyryl ethyl carbonate 0.9

Comparison of the data in Tables I and II show that although the O-acylalkyl carbonates are effective in both fuels, equivalent concentrationsof the same compounds are more effective in the higher octane fuel.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof and, therefore, only such limitations should be imposed asare indicated in the appended claims.

We claim:

1. A hydrocarbon fuel in the gasoline boiling range containing anorgano-lead anti-knock agent, at least 5.0 volume percent high octanecomponents selected from the group consisting of olefinic hydrocarbons,aromatic hydrocarbons and mixtures thereof and an O-acyl alkyl carbonatehaving the general formula:

1 if Ro -O O-O R wherein R denotes a hydrocarbyl radical containing 1-29carbon atoms and R is an alkyl group containing 1-10 carbon atoms, saidcarbonate being present in a concentration between 0.1 and 5.0 volumepercent, which concentration is sufficient to effect substantial octaneappreciation of said leaded fuel.

2. A hydrocarbon fuel according to claim 1 in which said organo-leadanti-knock agent is present in a concentration between 0.5 and 4.6 cc.per gallon.

3. A hydrocarbon fuel according to claim 1 in which said O-acyl alkylcarbonate is present in a concentration between 0.2 and 2.0 volumepercent.

4. A hydrocarbon fuel in the gasoline boiling range 0 nil-oiLo R whereinR denotes a hydrocarbyl radical containing 1-29 carbon atoms and R is analkyl group containing 1-10 carbon atoms, said O-acyl alkyl carbonatebeing present in a concentration between 0.1 and 5.0 volume percent,said concentration being sufficient to efiect substantial improvement inthe octane rating of said fuel.

5. A hydrocarbon fuel according to claim -4 in which said O-acyl alkylcarbonate is present in a concentration between 0.2 and 2.0 volumepercent.

'6. A hydrocarbon fuel according to claim 4 in which said high octanecomponents constitute 20-80 volume percent of said fuel.

7. A hydrocarbon fuel according to claim 4 containing 1.0 to 4.6 cc. ofTEL per gallon.

-6 8. A hydrocarbon fuel according to claim 4 in which said O-acyl alkylcarbonate is O-propiony1 ethyl carbonate.

9. A hydrocarbon fuel according to claim 4 in which said O-acyl alkylcarbonate is O-n butyryl ethyl carbonaoe.

References Cited in the file of this patent UNITED STATES PATENTS1,692,784 Orelup et a1. Nov. 20, 1928 2,210,942, Lipkin Aug. 13, 19402,360,585 Ross et al. Oct. 17, 1944 FOREIGN PATENTS 640,311 France Mar.26, 1928 837,965 France Nov. 28, 1938 72/1958 Trinidad and Tobago Oct.9, 1958 OTHER REFERENCES Improved Motor Fuels Through SelectiveBlending, by Wagner et al., paper presented before the 22nd AnnualMeeting of the American Petroleum Institute, November 7, 1941.

1. A HYDROCARBON FUEL IN THE GASOLINE BOILING RANGE CONTAINING ANORGANO-LEAD AND ANTI-KNOCK AGENT, AT LEAST 5.0 VOLUME PERCENT HIGHOCTANE COMPONENTS SELECTED FROM THE GROUP CONSISTING OF OLEFINICHYDROCARBONS, AROMATIC HYDROCARBONS AND MIXTURES THEREOF AND AN O-ACYLAKYL CARBONATE HAVING THE GENERAL FORMULA: